X-ray vidicon tube having screen hermetically sealed to envelope



Nov. 22, 1966 M. ROME ETAL 3,287,581

X-RAY VIDICON TUBE HAVING SCREEN HERMETICALLY SEALED TO ENVELOPE FiledApril 50, 1962 INVENTORS MART/N ROME HAROLD OWJORDAN United StatesPatent 3,287,581 X-RAY VIDICON TUBE HAVING SCREEN HER- METICALLY SEALEDT0 ENVELOPE Martin Rome and Harold 0. W. Jordan, Stamford, Conn.,

assignors to The Machlett Laboratories, Incorporated,

Springdale, Conn., a corporation of Connecticut Filed Apr. 30, 1962,Ser. No. 191,085 1 Claim. (Cl. 313-59) This invention relates to anX-ray vidicon and, more particularly, to a novel X-ray vidicon windowassembly.

The application of television techniques to X-ray pick-up devices hasnecessitated utilizing a window minimum X-ray absorption in place of theconventional glass window as the vacuum-tight terminating element.Beryllium metal, noted by its low X-ray absorption characteristics, isan ideal wind-ow for use in X-ray sensitive pick-up tubes, particularlyin applications involving low X-ray energy level incident radiation. Thelow X-ray absorption of beryllium metal, compared to glass, enhances thesensitivity of the camera tube, particularly at low energy levels,simply by permitting more radiation to become incident on thephotoconductive surface.

However, beryllium surfaces cannot be conveniently prepared with thehigh degree of uniformity and polishing required for high resolutionpick-up tubes. Both the microcrystalline structure and the protectiveoxide layer are detrimental influences on the selenium photoconductorsubstrate used with the beryllium window. That is, if the seleniumphotoconductor is vaporized directly onto the beryllium metal, thereoccurs a detrimental recrystallization of the selenium from theamorphous to a lower resistivity crystalline form due, at least in part,to the beryllium.

Accordingly, it is a primary object of our invention to providestructures in which the beryllium window may be sealed to a glass bulbforming the vacuum-tight envelope for the camera tube.

Another object of our invention is to provide a means for preventing areaction or change in crystal structure by interposing a barrier layerbetween the beryllium and selenium.

Still another object of our invention is to provide a smooth polisheduniform substrate for the selenium without a substantial increase inX-ray absorption.

Yet another object of our invention is to provide a thin smooth uniformmetallic substrate for the selenium that is an exact replica of theoriginal beryllium surface and which may be more'readily polished thanthe refractory beryllium.

A further object of our invention is to provide a thin, metallic,thermally conductive substrate which will also meet the requirements oflow X-ray absorption and a smooth uniform surface.

A still further object of our invention is to provide a smooth, uniform,thermally conductive substrate for the selenium without a substantialincrease in X-ray absorption.

The features of our invention, which we believe to be novel, are setforth with particularity in the appended claim. Our invention itself,however, both as to its organization and method of operation togetherwith further objects and advantages thereof, may be best understood byreference to the following description, taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a partial sectional view of our basic face-plate structure foran X-ray vidicon, and

FIG. 2 is a sectional view of a schematic representation of our novelberyllium window structure as used in a typical X-ray Vidicon.

Referring now to FIG. 1, there is shown the basic struc- Patented Nov.22, 1966 ture utilizing a beryllium window in an X-ray Vidicon. In thebasic structure, there is provided an envelope 16. A cylindrical ring18, having the same configuration as envelope 16, is affixed to the endof the envelope by means of the Tf-shaped solder ring 20. Around thecross-bar portion of the T-shaped indium solder is a stainless steelring 24. The whole assembly comprises Window assembly 13.

The window assembly is formed by joining beryllium window 14 to thekovar or monel ring 18. It has been found that monel is preferred sinceit is more easily brased than kovar and lends itself more readily togrinding and polishing. Grinding and polishing the mating surfaces isessential for the cold seal technique that is utilized in thisinvention. Having provided the seal between the beryllium and the monelring the window assembly 14, 18 is sealed to the edge of envelope 16 bymeans of indium solder 20. The indium or indium alloy is first cast orjoined to the inside surface of the stainless steel ring 24. The indium,which is soft and pliable, may be formed by machining or any otherwell-known means to the precise and desired configuration.

The indium stainless steel assembly 20, 24 is then interposed betweenthe monel ring 18 and the envelope 16 and the window assembly is joinedto the envelope by simultaneously applying a uniform pressure to bothring 18 and envelope 16.

Referring now to FIG. 2, it will be seen that when uniform pressure isapplied to the mating surfaces of ring 18 and envelope 16, that portionof the solder lying therebetween is squeezed out into the inside of theenvelope to form a shelf having upper and lower surfaces 10 and 12,respectively. It now becomes obvious that a photoconductive layer and abarrier layer (if necessary) may be applied to the under surface ofberyllium layer 14 in accordance with the principles set forth in ourc-opending application Serial No. 191,099 filed April 30, 1962 andentitled X-Ray Vidicon Assembly and Method.

FIG. 2 shows our invention incorporated in a typical X-ray Vidicon-typetube. The basic structure 13 is shown having ring 18 sealed to envelope16, as previously described. The wall 16 and the structure 13 togethercomprise a vacuum-tight envelope having an electron gun 40 mounted inone end thereof. The components that make up gun 40 include the usualcathode 42, control electrode 44, and one or more acceleratingelectrodes 46, all of which are connected to lead-in means 48 in awell-known manner. An electron beam 50 emanating from gun 40 is directedonto the target 62 of photoconductive material at the other end ofenvelope 10, and means is provided for focusing beam 50 and scanning itover the photoconductor 62. Such means may include a focussing coil 52,a deflection yoke 54 and an alignment coil 56, all of which are arrangedapproximately as shown. Another electrode such as grid 58 having asuitable potential applied thereon is positioned adjacent thephotoconductive material 62 and, in operation, functions cooperativelywith focussing coil 52 to insure that electron beam 50, in its finalapproach to the surface 62, is normal thereto. A final acceleratingelectrode 60 is also provided and may take the form of a metalliccylinder or a conductive coating painted on the interior wall of theenvelope between electrodes 46 and 58. The lead-in means 48, not shownin detail, are provided for the purpose of connecting electrode 60 aswell as the gun electrodes 42, 44, and 46 to the appropriate source ofelectrical potential located externally of the tube.

While there has been described what is presently considered a preferredembodiment of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the inventive concept contained therein, and it is,therefore, aimed in the appended claim to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

An X-ray vidicon tube comprising a glass envelope having one open endshaped to an annular configuration, and a window assembly mounted oversaid open end of the envelope comprising a metal ring and a berylliumdisc sealed throughout its periphery within the ring, the ring havinginner and outer surface configurations substantially the same as theannular open end of the envelope and superimposed thereon, brazingmate-rial sealing the ring to the open end of the envelope, metal meansencircling the brazing material, an X-ray sensitive target on the in- 154- ner surface of the window assembly, and an electron beam-formingdevice in the envelope for scanning the target with electrons.

References Cited by the Examiner UNITED STATES PATENTS 2,394,984 2/1946Claussen 31359 X 2,909,686 10/1959 Zunick 313-49 2,951,962 9/1960 Milleret al 313-65 10 3,061,664 10/1962 Kegg 31365X HERMAN KARL SAALBACH,Primary Examiner.

S. CHATMON, J R., Assistant Examiner.

